bugfix: dummy test application needs crm_connector initializer
updates and extends README

+ minor styling change to stay on 100 character line
updates base classes and their attributes

+ removes show_in_navigation from Root, Website, BoxText and BoxImage
+ adds sort_key to ContentPage
allows to check if an obj_class or attribute already exists in the CMS

+ the caller can handle what should happen, if it does not exist by rescue from DuplicateResourceError
+ adopts existing generators (kickstart, attribute, google_analytics and model)
updates google analytics to use variables set in the generator
bugfix: used wrong homepage path

+ refactored paths into variables
Merge branch 'feature/check-structure-exists' into develop

* feature/check-structure-exists:
  bugfix: used wrong homepage path
  updates google analytics to use variables set in the generator
  allows to check if an obj_class or attribute already exists in the CMS
Merge branch 'develop' into feature/dashboard

* develop:
  bugfix: used wrong homepage path
  updates google analytics to use variables set in the generator
  allows to check if an obj_class or attribute already exists in the CMS
  updates base classes and their attributes
  updates and extends README
  bugfix: dummy test application needs crm_connector initializer
corrects spelling and adds links to cms and crm news